固定床中纤维素热解及其焦油裂解机理研究

研究了500~900℃条件下微晶纤维素在固定床中的热解过程;分别采用气质联用(GC-MS)和气相色谱分析了热解过程中生成的焦油和不可凝气体。结果表明,随热解温度升高,焦油产率减少、气体产率升高、焦产率略微下降,同时CO、CH4和H2的产率明显升高,而CO2的产率变化不明显。焦油主要由二次反应产生,不可凝气体则由一次热解产物和二次热解产物共同产生。使用Gaussian 09软件对热解过程进行了模拟,发现纤维素分子在热解过程中首先分解为纤维素单体,然后纤维素单体上的羟基官能团优先脱除,生成的中间产物重组生成焦油。随热解温度升高,焦油中醚、醇、酸等化合物分解成自由基,自由基间发生重组、结合,导致烯烃和炔烃增多以及不可凝气体含量的升高。

Mechanism of cellulose pyrolysis and tar decomposition in a fixed bed reactor

Cellulose pyrolysis was studied in a fixed bed reactor at 500~900 ℃; the tar and gaseous products were analyzed by GC-MS and gas chromatograph, respectively. The results showed that the yield of gaseous products increases and that of tar and char decreases with the increase of pyrolysis temperature; the yield of CO, CH₄ and H₂ is increased significantly, while the yield of CO₂ is almost not altered. Tar is generated by the secondary reactions, while the non-condensable gases are generated by both the primary and secondary pyrolysis products. The mechanism of tar decomposition was considered through calculation with Gaussian 09, which suggests that cellulose is cleaved into cellulose monomer at the beginning of pyrolysis process. The hydroxy functional groups are removed from cellulose monomer preferentially, and then the intermediates are reformed into tar. With the increase of temperature, ethers, alcohols, acids and other compounds in tar are decomposed into free radicals; the amounts of alkenes, alkynes and non-condensable gases formed are then increased because of the reformation of free radicals at high temperature.